1. Field of the Invention
The present invention relates to a motor control apparatus with a current sensor diagnostic apparatus and a diagnostic method adopted for performing diagnosis on an abnormality at a current sensor used in an inverter.
2. Description of the Related Art
There are apparatuses proposed in the known art that perform diagnosis on an abnormality at a current sensor used in an inverter which detects three-phase currents IU, IV and IW by employing three current sensors and implements vector control on a three-phase AC motor (see Japanese Laid-Open Patent Publication No. H6-253585). This type of diagnostic apparatus performs diagnosis on a current sensor abnormality based upon the fact that the sum (IU+IV+IW) of the three-phase alternating currents at a given point in time in the three-phase AC motor is logically 0. Namely, it determines that a current sensor abnormality has occurred if the sum (IU+IV+IW) of the three-phase alternating currents detected at a single point in time by the three current sensors exceeds a judgement reference value.
Since the sum (IU+IV+IW) of the three-phase alternating currents at a given point in time in a three-phase AC motor is logically 0, any two-phase currents among the three-phase alternating currents may be detected to ascertain the remaining one-phase current through an arithmetic operation based upon the two detected currents. Thus, vector control may be implemented in the three-phase AC motor by employing only two current sensors.
However, with only two current sensors, a current sensor abnormality cannot be diagnosed by adopting the diagnostic method described above to implement vector control on a three-phase AC motor. Namely, since the current value of the remaining one-phase is determined based upon the premise that the sum (IU+IV+IW) of the three-phase alternating currents is 0 at a given point in time, the sum (IU+IV+IW) of the three-phase alternating currents never exceeds the judgement reference value. Thus, with only two current sensors, vector control can be implemented but a current sensor abnormality cannot be diagnosed.
An object of the present invention is to provide a current sensor diagnostic method and a motor control apparatus with a current sensor diagnostic apparatus to be adopted in conjunction with an inverter which implements vector control on a three-phase AC motor by utilizing two current sensors.
The motor control apparatus with a current sensor diagnostic apparatus according to the present invention comprises two current sensors which detect a first-phase current value and a second-phase current value among three-phase alternating currents flowing to a three-phase AC motor, an inverter which implements drive control of a three-phase AC motor based upon the first-phase current detection value and the second-phase current detection value among the three-phase alternating currents flowing to the three-phase AC motor detected by two current sensors and a judging unit which judges whether one of the current sensors is abnormal if either the absolute value of the deviation of the first-phase current detection value relative to a first-phase current command value or the absolute value of the deviation of the second-phase current detection value relative to a second-phase current command value exceeds a first judgement reference value during drive of the three-phase AC motor.
A current sensor diagnostic method for implementing current sensor diagnosis for an inverter which implements drive control on a three-phase AC motor based upon a first-phase current detection value and a second-phase current detection value among three-phase alternating currents flowing to said three-phase AC motor detected by two current sensors comprises calculating a first absolute value of a deviation of the first-phase current detection value relative to a first-phase current command value, calculating a second absolute value of a deviation of the second-phase current detection value relative to a second-phase current command value and determining one of said current sensors to be abnormal if either the first or second absolute value exceeds a first judgement reference value while said three-phase AC motor is being driven.